1. Field of the Invention
This invention relates to a ventilation system. In particular, it relates to a passive ventilation system with heat recovery for a building. It also relates to a heat exchange for a heat recovery ventilation system. The invention also relates to a method of installing a ventilation system in a building.
2. Description of Related Art
As buildings are becoming better insulated and more airtight, the need for adequate ventilation, to maintain a healthy indoor environment, is important. As many buildings are heated to temperatures above that of the outside temperature, ventilation systems can be the source of significant heat loss. Thus, warm “stale” air from inside the building is vented to the atmosphere, while colder “fresh” air is drawn in from outside. The building's heating system then has to work harder to warm the incoming cold air and maintain an even temperature.
Ventilation systems with heat recovery are known. These systems comprise an outflow duct and an inflow duct and a heat exchange. A first electric fan is used to move air from inside the building to the outside through the outflow duct, while a second electric fan is used to bring fresh air inside through the inflow duct. The heat exchange comprises a region where the inflow duct and outflow duct are separated by a thin membrane that allows heat transfer therethrough. Thus, the warm outgoing air is used to heat the cooler incoming air. These systems have been shown to be able to recover up to 80% of the energy of the outgoing air. These systems can therefore provide ventilation without a significant effect on heating requirement. However, if we take account of the electricity used by the fans, the overall saving in energy usage is very small.
For example, in a typical dwelling of 150 m2 with a standard ventilation system operating at 60 liters per second, and assuming an average 10 degree temperature difference between the inside and outside temperatures will increase the energy usage by 5140 kWh. Using a heat recovery ventilation system will save approximately 4100 kWh (i.e. 80%). However, a typical known heat recovery system will use approximately 900 kWh in electricity for the fans. Thus, the total saving in energy consumption is very small.